Long Term Evolution (LTE)/LTE-Advanced (LTE-A) is the mainstream fourth generation (4G) mobile communication technology. LTE/LTE-A is divided into the following two different duplex modes: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). A frame structure of Frequency Division Duplex is referred to as Frame structure type 1, and a frame structure of Time Division Duplex is referred to as Frame structure type 2.
FIG. 1 is a schematic diagram showing Frame structure type 1 in the prior art. As shown in FIG. 1, Frame structure type 1 is illustrated as follows: each radio frame has a length of Tf=307200·Ts=10 ms (millisecond) and is consisted of 20 slots; each slot has a length of Tslot=15360·Ts=0.5 ms (millisecond), with Ts being a time unit, Ts=1/(15000×2048) second, and the slots being numbered as 0 to 19; a subframe is defined as consisted of two consecutive slots, that is, subframe i is consisted of slots 2i and 2i+1; for FDD, during the time interval of 10 milliseconds, 10 subframes are used for downlink transmission, and 10 subframes are used for uplink transmission; the uplink transmission and the downlink transmission are carried out on different frequencies respectively; in half-duplex FDD mode, a user equipment (UE, for short) cannot transmit and receive simultaneously. However, in full duplex FDD mode, there is no such restriction.
FIG. 2 is a schematic diagram showing Frame structure type 2 in the prior art. As shown in FIG. 2, Frame structure type 2 is illustrated as follows: each radio frame has a length of Tf=307200·Ts=10 ms and is consisted of two half-frames; each half-frame has a length of 153600·Ts=5 ms and is consisted of 5 subframes, and each subframe has a length of 30720·Ts=1 ms; each subframe is defined as consisted of two slots, that is, subframe i is consisted of slots 2i and 2i+1, and the length of each slot is Tslot=15360·Ts=0.5 ms, Ts being a time unit, and Ts=1/(15000×2048) second.
The uplink-downlink configuration of a cell changes between frames, and uplink-downlink transmission occurs on the subframes of a frame. The uplink-downlink configuration of the current frame is obtained by a high-level signaling.
Table 1 shows 7 types of uplink-downlink configurations. For each subframe in a radio frame, “D” labels a downlink subframe for downlink transmission, “U” labels an uplink subframe for uplink transmission, and “S” labels a special subframe. A special subframe has the following three regions: a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS).
TABLE 1Downlink-Uplink-to-UplinkdownlinkSwitch-Config-pointSubframe numberurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
Table 2 shows the lengths of DwPTS and UpPTS. There are totally 10 types of special subframe configurations, and the total length of GP and UpPTS is 30720·Ts=1 ms.
It supports an uplink-downlink configuration with a downlink-to-uplink switch-point periodicity of 5 ms and 10 ms. In the case of a downlink-to-uplink switch-point periodicity of 5 ms, the special subframe lies in the two half-frames; and in the case of a downlink-to-uplink switch-point periodicity of 10 ms, the special subframe lies in the first half-frame. Subframes 0 and 5 and DwPTS are always used for downlink transmission. The subframe next to the UpPTS and the special subframe is used for uplink transmission. In the case of multi-cell or carrier aggregation, the guard period (GP) of the special subframe of a cell or a carrier employing frame structure type 2 has an overlap of at least 1456·Ts.
TABLE 2Downlink NCPExtended ECPUpPTSUpPTSSpecial SubframeUplinkUplinkUplinkUplinkConfigurationDwPTSNCPECPDwPTSNCPECP0 6592 · Ts2192 · Ts2560 · Ts 7680 · Ts2192 · Ts2560 · Ts119760 · Ts20480 · Ts221952 · Ts23040 · Ts324144 · Ts25600 · Ts426336 · Ts 7680 · Ts4384 · Ts5120 · Ts5 6592 · Ts4384 · Ts5120 · Ts20480 · Ts619760 · Ts23040 · Ts721952 · Ts12800 · Ts824144 · Ts———913168 · Ts———
Other subframes relative to the special subframe are normal subframes, and normal subframes are partitioned into downlink normal subframes and uplink normal subframe.
In LTE/LTE-A, downlink transmission employs Orthogonal Frequency Division Multiplexing (OFDM, for short) modulation technology, and data modulation occurs on a subcarrier in the frequency domain, and then a cyclic prefix is added when switching to the time domain, thereby consisting an intact time domain transmission OFDM symbol. The cyclic prefix (CP, for short) is provided for counteracting the symbol interference generated by multipath on the time domain and the inter-subcarrier interference generated on the frequency domain. In an LTE/LTE-A system, there are CPs with two different lengths: Normal cyclic prefix (NCP, for short) and Extended cyclic prefix (ECP, for short). An Extended CP is applied in a scenario with larger multipath time-delay extension. In the case of normal CP, the inter-subcarrier period is 15 kHz; and in the case of Extended CP, there are two types of inter-subcarrier periods, i.e., 15 kHz and 7.5 kHz, respectively.
The signal transmitted on each time slot is described with one or more resource grids, and a resource grid is consisted of NRBDLNscRB subcarriers and NsymbDL OFDM symbols. NRBDL represents the number of Physical Resource Blocks (PRBs) or Resource Blocks (RBs), NscRB represents the number of subcarriers in a Resource Block, and NsymbDL represents the number of OFDM symbols in a time slot. Table 3 shows the parameters of the Physical Resource Block, the number of OFDM symbols and the number of subcarriers on one RB. Table 4 shows the parameters of the OFDM symbol and the length of the cyclic prefix.
TABLE 3ConfigurationNscRBNsymbDLNormal Cyclic Prefix (NCP)Δf = 15 kHz127Extended Cyclic Prefix (ECP)Δf = 15 kHz6Δf = 7.5 kHz243
TABLE 4ConfigurationCP length NCP, lNormal Cyclic Prefix (NCP)Δf = 15 kHz160 for l = 0144 for l = 1, 2, . . . , 6Extended Cyclic Prefix (ECP)Δf = 15 kHz512 for l = 0, 1, . . . , 5Δf = 7.5 kHz1024 for l = 0, 1, 2
The number of Physical Resource Blocks NRBDL is determined by the downlink transmission bandwidth configured by the cell, with a minimum value of 6 and a maximum value of 110.
The same PRB on two successive slots on the same subframe is referred to as a PRB pair.
FIG. 3 is a schematic diagram showing a downlink resource grid in the prior art. As shown in FIG. 3, each unit in the resource grid is referred to as a resource element (RE, for short) and is labelled by an index pair (k,l), with k=0, . . . , NRBDLNscRB−1, representing the subcarrier sequence number on the frequency domain, and l=0, . . . , NsymbDL−1, representing the OFDM symbol sequence number on the time domain.
An antenna port is defined as a channel through which a symbol transmitted on the antenna port passes, and it may be predicted from a channel through which other symbols transmitted on the same port pass. The antenna port is further defined with a corresponding sequence number for distinguishing between the antenna ports and indexing the antenna port.
A downlink physical channel corresponds to a set of some resource elements, and it is provided for carrying the information from an upper level. Downlink physical information includes Physical Downlink Shared Channel (PDSCH, for short), Physical Multicast Channel (PMCH, for short), Physical Broadcast Channel (PBCH, for short), Physical Control Format Indicator Channel (PCFICH, for short), Physical Downlink Control Channel (PDCCH, for short), Physical Hybrid ARQ Indicator Channel (PHICH, for short) and Enhanced Physical Downlink Control Channel (EPDCCH, for short).
A Downlink Physical Signal corresponds to a set of resource elements, and it is used on the physical layer but not used for carrying the upper level information. The Downlink Physical Signal includes: Reference signal (RS), Synchronization signal and Discovery signal.
A Reference signal is also referred to as a pilot, including the following types: Cell-specific Reference Signal (CRS), Multimedia/Broadcast Single Frequency Network (MBSFN) Reference Signal, UE-specific Reference Signal (Demodulation Reference Signal (DMRS)), Positioning reference signal and Channel State Information-reference signal (CSI-RS). Further, UE-specific reference signal has the following two types: UE-specific reference signals associated with PDSCH and UE-specific reference signals associated with EPDCCH.
The CSI-RS is provided for a user equipment to predict the channel state. A CSI-RS transmitted with nonzero power is referred to as a nonzero power CSI-RS (NZP CSI-RS). In some cases, in order to avoid interference, it needs to transmit the CSI-RS with zero power to avoid the data transmission on some RE on the PDSCH, and this is referred to as zero power CSI-RS (ZP CSI-RS), the corresponding resource element set is Zero Power CSI-RS Resource. In some cases, in order to measure the interference, the CSI-RS is transmitted with zero power, and at this point, the corresponding resource element set is referred to as Channel-State Information-Interference Measurement Resource (CSI-IM Resource).
CSI reference signal (CSI-RS) configuration is provided for indicating an RE mapped by the CSI-RS, i.e., an RE used for transmitting the CSI-RS, and the CSI-RS configuration sequence number is provided for distinguishing between different CSI-RS configurations. The transmitting or mapping of an RE set of a CSI-RS under a CSI-RS configuration is referred to as a CSI-RS resource pattern. CSI-RS subframe configuration is provided for indicating the subframe on which CSI-RS transmission occurs.
A CSI-RS configuration is a CSI-RS configuration under a certain number of antenna ports, for example, a CSI-RS configuration with an antenna port number of 8 and a configuration sequence number of 0. A CSI-RS resource pattern is a CSI-RS resource pattern under a certain number of antenna ports. For example, a CSI-RS resource pattern with an antenna port number of 8 and an index of 0. Generally, the configuration sequence number is the index.
An RE set of a CSI-RS transmitting or mapping a part of the ports under the CSI-RS configuration is referred to as a partial port RS resource pattern. For example, a port RS resource pattern with a port sequence number of {15,16,17,18}.
CSI-RS with a port number of 1, 2, 4 and 8 is supported in the prior art, and CSI-RS resource patterns of these port numbers are repeated on each PRB pair in the range of the bandwidth on the transmission subframe.
The RE sets of the CSI-RS resource patterns of all the configurations with different port numbers are the same, i.e., the RE set of the CSI-RS resource pattern of all the configurations with a port number of 2 equals to the RE set of the CSI-RS resource pattern of all the configurations with a port number of 4 and equals to the RE set of the CSI-RS resource pattern of all the configurations with a port number of 8. For example, for the common CSI-RS configuration of Frame structure type 1 and Frame structure type 2, the RE sets of the CSI-RS resource pattern of all the configurations with different port numbers are the same, and the RE number on one PRB pair is 40.
FIG. 4 is a schematic diagram showing a resource pattern of a CSI-RS with a port number of 4 on an RB pair in the prior art, and FIG. 5 is a schematic diagram showing a resource pattern of a CSI-RS with a port number of 8 on an RB pair in the prior art, as shown in FIG. 4 and FIG. 5.
In order to make full use of the power and improve the precision of channel measurement, the CSI-RS of each port is further divided into groups, i.e., one of the groups includes the CSI-RS of a plurality of ports, and there are groups of different numbers from one to many. The CSI-RS of each port in a group may be mapped to a group of common REs in a code division multiplexing mode. For example, the port number in the group is N, and the CSI-RS sequence is {r0,r1,L,rN-1}; there further exist a sequence group {w0p,w1p,L,wN-1p} with a length of N, with p=K+0, K+1, . . . , K+N−1, and there are N sequences in the group, which are orthogonal to each other, i.e., Σm=0N-1wmiwmj=0, with i, j=K+0, K+1, K+N−1 and i≠j; sequence {w0p,w1p,L,wN-1p} is modulated by CSI-RS sequence {r0,r1,L,rN-1} to obtain a CSI-RS sequence {r0w0p,r1w1p,L,rN-1wN-1p} with a port of p. Corresponding to a group of common REs, the elements in the CSI-RS sequence with the port of p are mapped to REs in a one-to-one correspondence. N is the length of multiplex.
In the prior art, the CSI-RS between the ports is multiplexed and mapped to the RE in the following mode: the ports are divided into groups, such as totally four groups of {15,16}, {17,18}, {19,20} and {21,22}. The four groups are multiplexed to the RE in a Frequency Division mode; but the CSI-RSs on the ports in the group are multiplexed to the RE in a Code Division mode. For example, the CSI-RS of port 15 and the CSI-RS of port 16 are multiplexed in Code Division mode on the time domain.
The base station notifies information on the user equipment of the CSI-RS information via an upper-level signaling. The information includes: a CSI-RS resource configuration identity, a CSI-RS port number, a CSI-RS configuration and a CSI-RS subframe configuration.
There are four types of scenarios for CSI-RS transmission. The first type is used in the case of NCP, and it may be not only provided for transmitting a CSI-RS on Frame structure type 1, but also provided for transmitting a CSI-RS on Frame structure type 2, where CSI-RSs of 4 ports, i.e., with port numbers of 0, 1, 2, 3, may be transmitted on the transmission subframe.
The second type is used in the case of NCP, and it may be only provided for transmitting a CSI-RS on Frame structure type 2, where CSI-RSs of 2 ports, i.e., with port numbers of 0, 1, may be transmitted on the transmission subframe, while CRSs of port numbers 2, 3 cannot be transmitted.
The third case is used in the case of ECP, and it may be not only provided for transmitting a CSI-RS on Frame structure type 1, but also provided for transmitting a CSI-RS on Frame structure type 2, where CSI-RSs of 4 ports, i.e., with port numbers of 0,1,2,3, may be transmitted on the transmission subframe.
The fourth case is used in the case of ECP, it may be only provided for transmitting a CSI-RS on Frame structure type 2, where CSI-RSs of 2 ports, i.e., with port numbers of 0, 1, may be transmitted on the transmission subframe, while CRSs of port numbers of 2, 3 cannot be transmitted.
As the number of antennas increases, a larger gain may be brought to a radio system. However, RE overhead would be added when reference signals of a larger number of antennas are transmitted. In the case that the RE number provided by each RB for CSI-RS overhead on the downlink normal subframe is determined, the multiplexed number of the CSI-RS decreases, which would affect the coordination of CSI-RS transmission between cells, thus increasing the complexity of coordination, and introducing a larger interference to channel measurement.
When a CSI-RS is transmitted on DwPTS, resources for transmitting the CSI-RS may be added, so that the multiplexed number of the CSI-RSs may be increased. At present, there is still a problem on how to support the transmission of a CSI-RS in DwPTS in the above four types of scenarios for CSI-RS transmission. Moreover, there are also two problems on transmitting CSI-RS in DwPTS: One is that the CSI-RS is only transmitted on DwPTS under one CSI-RS resource configuration; and the other is that the CSI-RS is transmitted not only in the DwPTS but also on a downlink normal subframe under one CSI-RS resource configuration. For example, the period of the DwPTS is 10 ms, and if the CSI-RS needs to be transmitted on DwPTS and the transmission period of the CSI-RS is 5 ms, the CSI-RS is not only transmitted on DwPTS, but also transmitted on the downlink normal subframe. This will complicate the transmission of CSI-RS in DwPTS.
For the problem of transmitting CSI-RS in DwPTS in a CSI-RS transmission scenario of the prior art, there is no effective solutions at present.